Document Detail

On the chiroptical behavior of conjugated multichromophoric compounds of a new pseudoaromatic class: bicolchicides and biisocolchicides.
MedLine Citation:
PMID:  20485544     Owner:  NLM     Status:  MEDLINE    
BACKGROUND: It is well known that, stemming from the mutual interplay between chromophores, circular dichroism (CD) is a powerful technique to deal with structural problems for both the small organic molecule and the biopolymer. However, quantitative interpretations of the spectroscopic and structural terms that give rise to the exciton couplet are usually presented for ideal cases, or a few CD bands only are taken into account, overlooking the role of the solvent medium.
METHODOLOGY/PRINCIPAL FINDINGS: Circular dichroism and UV absorption spectra were carried out for colchicide (3) and isocolchicide (6), as well as their coupling products, 10,10'-bicolchicide (2) and 9,9'-biisocolchicide (5), in both hydrogen bonding and non hydrogen bonding solvents, as well as MeCN/H(2)O mixtures. A dramatic control by the solvent emerged, as even tiny changes in the composition of solvent mixtures, at ca 1 water molar fraction, induced a dramatic modification of their CD bands. A mutarotation phenomenon--long known for isocolchicine (8)--was also observed for 5, and can be attributed to the interconversion between atropisomers (R(a),7S),(R(a),7'S)-5a and (R(a),7S),(S(a),7'S)-5b.
CONCLUSIONS/SIGNIFICANCE: Our data show that with molecules built on two structurally identical moieties which embody both hydrophilic and hydrophobic groups, even tiny changes in the composition of solvent mixtures cause a dramatic modification of the CD bands. Their analysis arrives at a qualitative rationalization of the observed CD couplets from the coupling of high energy transitions, while attempts at a quantitative interpretation of these phenomena through time-dependent density functional theory allowed to reproduce satisfactorily the CD spectrum in the 300-450 nm region only. Failure with higher energies probably reflects currently inadequate specific theoretical treatments of the solvent medium.
Tiziana Funaioli; Marino Cavazza; Maurizio Zandomeneghi; Francesco Pietra
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2010-05-12
Journal Detail:
Title:  PloS one     Volume:  5     ISSN:  1932-6203     ISO Abbreviation:  PLoS ONE     Publication Date:  2010  
Date Detail:
Created Date:  2010-05-20     Completed Date:  2010-09-07     Revised Date:  2011-02-03    
Medline Journal Info:
Nlm Unique ID:  101285081     Medline TA:  PLoS One     Country:  United States    
Other Details:
Languages:  eng     Pagination:  e10617     Citation Subset:  IM    
Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Pisa, Italy.
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MeSH Terms
Chromatography, High Pressure Liquid
Circular Dichroism
Colchicine / analogs & derivatives*,  chemical synthesis,  chemistry,  isolation & purification
Hydrocarbons, Aromatic / chemical synthesis,  chemistry*,  isolation & purification
Spectrophotometry, Ultraviolet
Reg. No./Substance:
0/Hydrocarbons, Aromatic; 30771-10-9/isocolchicine; 518-15-0/colchicide; 64-86-8/Colchicine
Erratum In:
PLoS One. 2010;5(7) doi: 10.1371/annotation/c8a83120-e963-40f4-8591-90bd7f0c6b37

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